This invention concerns, in general, the sector of semiautomatic and automatic shotguns with the so-called xe2x80x9cgas-flowxe2x80x9d operation, and, in particular, those guns furnished for purposes of functionality, reliability and durability with automatic compensation of the gas thrust on the moving parts, such as arming rods, breech-block, breech-block carriage, all intended to give the best possible constant working conditions.
Here below, reference will be made especially to smooth bore shotguns of the type used for hunting, for which the invention, although of a general nature, is primarily intended.
Automatic or semiautomatic shotguns with a gas-flow device already exist. It should be noted that a semiautomatic shotgun with a smooth bore, in particular, can be used to shoot a very wide range of cartridges. For example, the range starts with the 12 caliber/gage, with 24 gram cartridges, typically used in clay-pigeon shooting, up to the powerful 56 gram and even 64 gram cartridges in the versions with the 3xc2xd inch super magnum cartridge chamber. Such a wide range means a great variety of working conditions. As a result of this requirement, the xe2x80x9cgas-flowxe2x80x9d device of the latest versions is often equipped with a special valve, used to xe2x80x9cparalyzexe2x80x9d the impulse of the venting gases when firing the most powerful cartridges. This has the aim of keeping the rearming speed of the moving parts within acceptable limits and, thereby, avoids premature breakage due to the excessive strain on components. Although various types of automatic compensation valves have been developed over the years, today there is a standardization of the working principle. The compensation effect is achieved by means of venting the gas once a pressure limit inside the gas-flow cylinder has been reached; beyond this pressure, the valve, which is normally kept closed by a spring, allows a certain quantity of gas to be discharged.
The main characteristics required of a gas-flow device are:
the performance, that is, the capacity for maintaining the shotgun working conditions as constant as possible, irrespective of the cartridge power, and ideal for carrying out the rearming and loading and for ensuring an acceptable life-span for the parts subject to mechanical stress. The valve must remain closed and hermetically sealed against leaking gas during the firing of less powerful cartridges in order to guarantee sufficient rearming speed, then open progressively as the power of the cartridge being fired increases; the seal, that is, the capacity for keeping to a minimum the passage of gases between the piston and cylinder which are vented from the barrel and necessary for the rearming of the moving parts;
the lightness, simplicity and economy of construction;
the reliability, intended as maintaining the calibration and, above all, as the capacity for self-cleaning of the solid residues of the gas combustion. This condition, if not obtained, may cause the devices to lose their functionality and, consequently, oblige the user to undertake frequent and costly maintenance. If this maintenance is not carried out, dangerous situations may arise due, for example, to the partial or total blockage of the venting holes, or a diminution of the duration of the various components;
the possibility of adapting to various gun shapes, like the shape which is particularly sought after because it imposes no limits on the number of shots available, where the magazine passes inside the gas-flow cylinder and where the expansion chamber consequently assumes the characteristic ring shape.
The current state of the art is such that there is no case in which the above-mentioned characteristics, which may be referred to briefly as self-compensating gas-flow device and self-cleaning with loop magazine, are all present in the same version.
Given the above, it is the aim of this invention to supply a gas-flow device, in particular, for semiautomatic smooth bore shotguns, incorporating as far as possible the characteristics mentioned above and which can be summarized as follows:
an optimal self-compensation to give the gun components longer life;
a self-cleaning function for the compensation valve and the piston sealing elements, giving a practically maintenance-free operation, while making the device safer and more reliable at the same time; and
a construction which is simple, light and economic in the version with the loop magazine, and, therefore, unaffected by limits of ammunition capacity.
This object and the advantages which derive from it are achieved with a gas-flow device for semiautomatic smooth-bore shotguns and a loop-type magazine in a gas-flow cylinder that has a pressure-type valve, with a ring shape, associated with the cylinder, placed around the magazine and held in a closed position by a spiral spring, suitably pre-stressed, and a valve with self-cleaning means on its rest plane.
With such a low-inertia ring valve, the gas-flow device has optimal self-compensation, given that the initial pre stressing of the spring is such as to keep the valve closed and prevent gas from being discharged from the gas-flow cylinder when firing weak cartridges, and to allow a gradual opening in proportion to the strength of the cartridges, thereby allowing a partial venting of gases at the higher pressures and maintaining the speed of the moving parts within optimal values.
The self-cleaning action is achieved by both a special shape of the valve rest/support plane, which exploits the principle of mechanical removal of the dirt after each shot, thanks to the valve motion with respect to the gas-flow cylinder due to the spring action in opening/closing the valve itself, and by self-cleaning means of the piston sealing elements, which exploit the direct action of the venting gases.
The ring shape of the compensation valve is such that it can be placed around the magazine, without interfering with the latter, either radially or lengthwise. This is a particularly valued characteristic because, apart from permitting the usual loading of an extra shot, it means that other magazine extensions may be added in the future, to give an even better capacity than the one in question. Such a set-up, therefore, makes the entire device light and simple, since it incorporates into one single mechanical part, the cylinder, all the following functions: the expansion of the gas; the sliding of the piston and the guide for the compensation valve; the attachment of the pre-stressing and gas-venting collar.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.